ARF (G-Protein)
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ARF is a monomeric member of the GTP-binding proteins, and has a function in cells to signal the assembly and disassembly of the coatomer coat of some vesicles.
[edit] Vesicle assembly
The ARF molecule releases its bound GDP and replaces it from GTP, which has been released by another protein in the cell membrane. This causes ARFs fatty acid tail to become exposed, and it inserts into the lipid bilayer..
The ARF molecule then recruits coatomer units, causing the assembly of a coatomer coat. This binding brings the membrane into a bud, which then pinches off to form a vesicle.
[edit] Vesicle disassembly
When the coatomer coat docks with the target membrane, a GTP-ase activating protein in the target membrane activates the GTPase of the ARF protein. Once ARF has hydrolysed its bound GTP, it undergoes a conformational change. This causes its fatty acid chain to disassociate from the vesicles membrane, and the coat disassembles.
It is thought that this mechanism ensures these vesicles only travel in one direction, as the protein in the target membrane that activates the GTPase action of ARF is only found in the target membrane, preventing the same vesicles fusing with a different target.
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